The purpose of this project is to study immune responses in man and animals to natural and experimental rickettsial infections, particularly Q fever, and to isolate and identify the causative pathogens. For serological investigations, recently developed procedures such as indirect immunofluorescence, microagglutination, and the enzyme-linked immunosorbent assays (ELISA) are being used. It also provides serologic support to other RML units and occasionally also to outside agencies, and includes serodiagnosis of other bacterial or viral diseases under investigation. For the isolation of pathogens, susceptible laboratory animals (meadow voles, guinea pigs, embryonated hen eggs, etc.) and various tissue culture systems (Vero, L cells, etc.) are being used. Serologic tests as well as immunochemical procedures (SDS-PAGE, western blotting) are applied to identification of isolates. The indirect IF test proved to be a valuable tool in early diagnosis of Q fever during a large outbreak in Switzerland. In spite of antibiotic therapy, Coxiella burnetii was found to destroy the aortic or mitral valves in patients with chronic Q endocarditis. It similarly affects the porcine valve replacement and causes detachment of the inserted plastic prosthesis. An unusual case of chronic Q fever endocarditis with neurological abnormalities was serologically diagnosed. After 25 years storage in aqueous suspension at 4 degrees C, the experimental RML Q fever vaccine (Q 58 A) was found to have retained its initial antigenic potency. Results of animal tests suggest that this vaccine also protects against C. burnetii from Q fever endocarditis patients.